1. Field of the Invention 07/553,640, 17, 1990,
The present invention relates to an information processing apparatus and a display system, and more particularly to an information processing apparatus for a liquid crystal display system employing ferroelectric liquid crystal with memory ability.
2. Related Background Art
In the field of display for computer terminals, there are principally employed cathode ray tubes of refresh scan type, and cathode ray tubes of vector scan type are partly used in large-sized high-resolution displays for CAD applications. The vector-scan cathode ray tubes, in which the image, once displayed, is not erased until the image frame is renewed, are not suitable for real-time man-machine interface displays requiring cursor movement, moving display of a pointing device such as a mouse, displays of editing (insertion deletion, movement, copying) with icons, characters and text etc. On the other hand, the refresh-scan cathode ray tubes require refreshing cycles with a frame frequency at least equal to 60 Hz for preventing flicker phenomenon, and employ non-interlaced scanning system for improving the visibility of moving display of the information in the image frame. (As already well known, television employs interlaced scanning system with a field frequency of 60 Hz and a frame frequency of 30 Hz for simplifying the moving image display and the drive control system.) For this reason, as the resolving power of display becomes higher, there are inevitably required a larger display unit, a larger power consumption, a larger drive control device and a higher cost.
In fact the recent development of flat panel displays is based on the inconvenience of bulkiness and high power consumption of the cathode ray tubes.
Presently there are known several types in the flat panel display. For example the twisted nematic liquid crystal-display with high time-divided drive (STN), its black-and-white version (NTN), or the plasma display employs same image data transfer method as in the cathode ray tubes, and the non-interlaced scanning method with a frame frequency at least equal to 60 Hz. Since such displays do not have memory ability in principle, there is required refreshing cycles with a frame frequency at least equal to 60 Hz for preventing flickering, so that the horizontal scanning time is 10 to 50 .mu.sec. or even shorter in case of a large display panel with 400 to 480 horizontal scanning lines constituting an image frame, and sufficiently high contrast cannot be obtained.
Ferroelectric liquid crystal display can provide a far larger panel size and a far higher resolution in comparison with the above-mentioned conventional displays, but, because of the low frame frequency, there is being required a partial rewriting scanning method (scanning only in the lines to be rewritten), exploiting the advantage of memory ability, in order to be applied to the man-machine interface displays as explained before. Such partial rewriting method is already disclosed for example by Kanbe et al. in the U.S. Pat. No. 4,655,561.
In the ferroelectric liquid crystal displays, the above-mentioned partial rewriting scanning method is suitable for the moving display for a mouse or a cursor, or for multi-window scroll display, but such partial rewriting scanning cannot be conducted in two areas at the same time. Consequently, in the partial rewriting scanning in an area designated by a start address and an end address, the moving display for mouse or cursor cannot be made in the course of multi-window scroll display. More specifically, for example in case of the window scroll display and the display for pointing device, if the pointing device is moved after the start of a partial rewriting scanning operation started in response to a request for window scroll display, the rewriting scanning operation for said pointing device cannot be started until the window scanning operation is completed to the last scanning line. Consequently the movement of the pointing device can only be displayed uncontinuously according to the size of window (number of rewriting scanning lines), so that the moving display becomes evidently unnatural.